Anatomically, teeth are aligned to and with each other in an arch form contacting each other on a mesial and distal side. The size, shape and tightness of these contacts is vital to the health of the teeth and supporting periodontal structures. As caries develop in the interproximal surfaces, there is a need to restore the surfaces to the proper anatomical form and to reestablish the appropriate contact points.
The typical practice, following cavity preparation, is to place a dental matrix band circumferentially around a tooth for filling and holding restorative material to achieve the proper contour. Dentists commonly use the dental matrix band with a matrix band retainer instrument which helps to position the band and to tighten it securely about the tooth. To adjust the fit of the band and to maintain it in a suitable position during restoration, other dental instruments, such as the triangular shaped wedge, are commonly used. The wedge may be inserted, just above the gumline, between the tooth being restored and an adjacent tooth. The wedge slightly separates the teeth to accommodate the thickness of the band and to create a seal at the end of the band to keep the filling material in place. It is also known in the art to use a sectional matrix ring system which fits between two teeth for applying contoured bands and establishing a tight contact.
Over the years, various types of devices have been developed to help distend the band during an initial composite curing period. While the conventional devices have added many advances to the field, they retain significant limitations. Perhaps the most common limitation of conventional devices is that the restoration tends to result with a narrow contact area at the marginal ridge. When the contact area is smaller in size than ideal, the restoration is weak and subject to fracture. It can leave a gap between the contact point, gum and neighboring teeth for food entrapment and infection. Devices designed to overcome contact weakness have been shown to be cumbersome in use and to provide inconsistent results. The wedge, for instance, is operated by hand and thus depends upon a variant level of torque which can be subject to human error. Once in position, the wedge can shift out of place. If made of wood, or similar porous material, it is prone to moisten with saliva and lose its effectiveness. The matrix ring instrument requires an ideal preparation to function correctly and tends to be cumbersome due to the need to engage multiple components. These devices can be cumbersome, time consuming and may even hinder the practitioners' view of the restoration.
In the past, the most common restorative material has been silver amalgam, a metal putty. Due to its strength, amalgam material maintains its shape. In this way, the amalgam filling material also functions to assist with the displacement of the dental matrix band into tight contact with the adjacent tooth. Today, with the advancements in dental materials, compactable composite resins are increasingly used. Unlike amalgams, composite resins do not have the condenseability necessary to displace the matrix band in position during restoration. As a result, the elastic memory of the band pulls away from the adjacent tooth thereby leaving a gap or space. The elastic memory exhibits a very flat proximal surface which, following restoration, yields a thin contact area at the marginal ridge. This result is clinically undesirable. The band is not well deformed to appropriate contour by composite material alone.